Microchannel plates are used as electron multipliers in image intensifiers. They are thin glass plates having an array of channels extending therethough and are located between a photocathode and a phosphor screen. An incoming electron from the photocathode enters the input side of the microchannel plate and strikes a channel wall. When voltage is applied across the microchannel plate these incoming or primary electrons are amplified, generating secondary electrons. The secondary electrons then exit the channel at the back end of the microchannel plate and are used to generate an image on the phosphor screen.
In general, fabrication of a microchannel plate starts with a fiber draw processes. An etchable core rod is drawn within a non-etchable silicate tube to form a round fiber comprised of a core rod and cladding layer. These fibers are then bundled and drawn into an equilateral hexagonal shaped pre-form known as a multi-fiber bundle. Each multi-fiber bundle can contain over 10,000 core rod sites. These hex-shaped multi-fiber bundles are packed into a glass packing tube and non-etchable hexagonally shaped support rods are packed between the bundles and the cylindrical wall to form a boule that is fused together in a heating process to produce a solid boule of rim glass and fiber optics. Subsequent process steps entail slicing, beveling, and polishing the glass boule into plates. Afterwards, the plates are etched to remove the core rods within the plates to thus form the channels, each of which is defined by the cladding layer. The channels are then activated and metallized.
Because of the geometries involved in the process described above, when the fibers are fused together the distance between the cylindrical inner wall of the glass packing tube 22 and the support rods 24 will vary. See FIG. 1 of the drawing. In other words, the interstitial space (or open space) between the outer most fibers and the inner surface of the glass packing tube is not constant. This variation means that the inner wall of the glass tube 22 will touch some rods 24 sooner than others during the fusion operation. This time-dependent touching of the fibers will cause the fiber bundles 16 and their individual fibers within the packing scheme to shift during the time period which occurs during the fusion operation. This shifting of the fibers causes the core rods within the bundles to move from the location established by each prior to the beginning of the fusion operation. Movement of the fibers closer together can lead to missing channel walls after the etch process because there will not be enough cladding glass to form a wall between the channels. These missing channel walls can lead to any number of defects such as ion barrier or film emission points, reduced structural integrity and ruptures.